The invention relates generally to silicon carbide devices and more particularly to silicon carbide MOS devices.
Silicon carbide (SiC) metal oxide semiconductor field effect transistors (MOSFETs) are currently being investigated because of silicon carbide's superior material properties with potential high power switching applications. SiC of 4H polytype is considered attractive for such applications due to its large band gap (3.26 eV), enabling blocking of large voltages with a smaller on resistance. SiC is a crystalline substance that can endure very high temperatures, which obviates the need for device cooling. SiC semiconductor devices can operate at temperatures in excess of 200° C. SiC also has high breakdown field, which is about ten times that of silicon, and a higher thermal conductivity, which is about three times that of silicon. These advantages can lead to reductions in weight, energy dissipation and volume at the system level in diverse applications such as aircraft engines and automotive hybrid vehicles. All types of sensor, logic (ICs), power control and power conditioning devices based on SiC should therefore prove to have advantages over analogous silicon (Si) devices.
A roadblock to realizing silicon carbide's potential has been the higher than expected on-resistance measured in SiC MOS devices. This is primarily due to lower than expected mobilities, both field effect mobility and Hall mobility (˜1 to 25 cm2/Vs for a Si face (0001) plane SiC 4H substrate), in silicon carbide inversion layers. The channel mobility (inversion layer mobility) in SiC MOSFETs affects the device conduction loss (thus efficiency) in SiC power MOSFETs.
One way this problem is being currently addressed is by using alternate SiC crystal face orientations, which have shown promise in improving the channel mobility. Others ways of increasing channel mobility include improving the oxidation process to improve the channel mobility. It would be beneficial to have additional techniques for increasing channel mobility.